FIELD OF THE INVENTION
Compounds of the formulas I and II are known as antibacterial agents as described in UK Patent Applications No. 2043639-A, 2097786-A, 2118181-A, 2133010-A, EP 0167100-A, EP 0166972-A, EP 0199446-A, EP 02011206-A and in European Patent Application No. 87 102825.4, filed on Feb, 27, 1987. ##STR1##
As described in the above cited patent applications and also in UK Patent Application No. 2144743 and in EP 0188247-A, compounds of formula I and II are prepared by different chemical syntheses. Alternatively, compounds of formula II can be prepared by esterification of compounds of formula I.
However, no practical method is presently available to transform compounds of formula II into compounds of formula I in good yield.
In order to avoid side reactions during the penem syntheses described in the above cited prior art, it is necessary to protect the 2-carboxy group. For this purpose, a group of formula --CHR.sub.3 --OCO--R.sub.4 may be employed.
In the above formula --CHR.sub.3 --OCO--R.sub.4, R.sub.3 is a hydrogen atom or a C.sub.1 -C.sub.6 alkyl group, and R.sub.4 is a hydrogen atom or an alkyl, alkenyl, alkoxy, phenyl, phenylalkenyl or phenylalkyl group having from 1 to 18 carbon atoms.
Moreover, such compounds of formula II are useful as orally adsorbed esters, as described in UK 2133010-A.
A simple conversion of compounds of formula II into compounds of formula I would allow for the preparation in a few steps of both the useful "in vivo+ hydrolyzable esters and the corresponding acids.
Further, it would also be desirable to have a method for converting a stored amount of a stable oral antibiotic drug of formula II into the corresponding acid or salt thereof, which could be formulated as a useful parenteral drug.
However, at present, no method is known which satisfies the above conditions.